44 



BROECKER 



TABLE 5 

 SEDIMENTATION RATES IN VARIOUS OCEAN WATERS 



*W = warm = 127,000 to 75,000 years ago. C = cold = 75,000 to 11,000 years ago. 

 tDissolution important. 



It turns out that there are only about five areas where we have reallv good 

 data (Table 5). If we focus our attention on the calcium carbonate total, we 

 notice that in each of these areas the difference in accumulation rate between 

 average glacial and average interglacial periods is discouragingly small. So the 

 system appears to be reasonably stable. If we go on to dissolution evidence, we 

 do see a difference. Everywhere we look, there is evidence of more severe dis- 

 solution of sediments during warm periods than during cold periods. For any 

 place in the ocean for which we have data, apparently the sedimentary carbonate 

 was more severely attacked by the waters at that spot during warm periods than 

 during cold periods. One of the methods that is used is to look at the ratio of 

 planktonic to benthic foraminifera in the sediments. Those which form on the 

 bottom are hardy and do not dissolve very well, and those which grow on the 

 surface are very fragile and dissolve very rapidly. When we subject a sediment to 

 solution in the laboratory or in nature, the planktonics disappear rapidlv and the 

 benthics disappear slowly or not at all. The original value of the ratio is about 50 

 falling from the surface to 1 living on the bottom. The ratio is reasonable 

 inasmuch as there is far more food available at the surface than there is at the 

 bottom. In the equatorial Pacific Ocean, there is a band of carbonate sediment 

 that is well below the compensation level. This sediment has been subject to 

 intense dissolution. If no benthics were dissolved, we could say that about 95% 

 of all the planktonic species had been destroyed by solution, during interglacial 

 times, whereas during the cold period only 50% of the planktonics were 

 dissolved. The same is true in the Indian Ocean; there is a much greater 



